Method of removing virus from water



Oct. 26, 1965 s. P, FELIX 3,214,369

METHOD OF REMOVING VIRUS FROM WATER Filed Dec. 21. 1961 INVENTOR. SAMUELP FELIX T ATTORNEYS United States Patent 3,214,369 METHGD 0F REMOVINGVIRUS FROM WATER Samuel P. Felix, Palo Alto, Calif., assignor, by mesneassignments, to De Laval Turbine Inc., Trenton, N.J., a corporation ofDelaware Filed Dec. 21, 1961, Ser. No. 161,157 1 Claim. (Cl. 210-24)This invention relates to a filtering process and apparatus for theremoval of virus from contaminated water.

Since viruses are difficult to detect, their removal cannot bedetermined with certainty. Moreover, chlorination is not alwayseffective in destroying viruses as contrasted with bacteria. Oneeffective technique for virus removal from water involves chemicalflocculation which results in the formation of a metal-virus complexwhich aggregates to form a separable precipitate. The formation of themetal-virus complex appears to be the result of a metal cation-proteinion reaction. The use of iron or aluminum salts, such as iron sulfate oraluminum sulfate, for the formation of the metal virus salts has beenfound to provide satisfactory results. The virus is not destroyed by thefiocculant but is concentrated in the floc.

In accordance with prior methods of removing the virus by flocculation,after the metal-Virus complex was formed and aggregated to form aprecipitate, the precipitate was detained in a coagulating basin toallow the coagulant to form aggregates of a sufiicient size so that theywould settle out by gravity. In this settling method, the size of thecoagulating and settling tank must be large enough to slow the liquidvelocity so that settling can take place. Thus, in the case of thepublic water supplies where large volumes of water must be handled,coagulating and settling tanks of extremely large sizes are required.Moreover, detention times of approximately three hours are normallyinvolved in these settling methods.

It is an object of this invention to provide a filtering process andapparatus involving the use of a filter, such as the diatomaceous earthtype, for the removal of virus from water. The method in accordance withthis invention makes use of the fact that the metal-virus complexformation is an ionic reaction which occurs instantaneously. Broadlyspeaking, the present invention involves admixture of the raw water andthe fiocculating agent in a detention tank for a very short time, onlysufiicient to insure uniform admixture of the contents and passing theliquid from the detention tank through a diatomaceous earth filter whichremoves the floc containing the virus. The detention time need only besufficient to permit the metal-virus complex to aggregate to a sizelarge enough to be filterable by the diatomaceous earth filter, whichcan remove particles of very small sizes (though it would not remove theunmodified virus).

The above and other objects and features of the invention will becomeapparent from the following description read in conjunction with theaccompanying drawing in which the single figure is a diagrammaticillustration of a filtering system provided in accordance with thisinvention.

The raw water is delivered to a detention tank through a line 12, havinga control valve 14 connected therein. A body feed tank 16 is providedand contains a slurry comprising pre-flocked diatomaceous earth and aheavy metal salt which is preferably iron sulfate. The diatomaceousearth should make up 4 to percent by weight of the mixture. It will beapparent that other metal cation flocculating agents may be used insubstitution for or in addition to iron sulfate, as for example aluminumsulfate, those used being, of course, nonice toxic. In the body feedtank, the iron sulfate hydrolyzes and deposits on the diatomaceousearth. The body feed tank 16 is connected to an eductor 18 through aline 20 having a control valve 22 connected therein. The eductor 18 isconnected in a line 24 which is connected between a line 26 and inletline 12 and has a control valve 28 connected therein. Line 26 isconnected to tank 30 which is elevated to provide a large pressure headon the rest of the apparatus and contains clean water which is suppliedfrom the ultimate reservoir. Line 26 has a control valve 32 connectedtherein. The slurry in tank 16 is drawn therefrom by the flow of liquidpassing from the storage tank 30 through line 26 and line 24 through theeductor 18. Thus, there may be provided in tank 10 a mixture of rawwater and the body feed slurry comprising the preflocked diatomaceousearth and iron sulfate. A conventional mixer 34 is mounted on detentiontank 10 and serves to agitate the liquid contained therein in order toprovide for good mixing of the raw water and the slurry from the bodyfeed tank 16. A similar mixer 36 is mounted on body feed tank 16 foragitating the slurry therein.

A line 38 is connected between the outlet of the detention tank 10 andthe inlet of a filter 40. The filter 40 may be of any suitable typeadapted for filtration by the use of diatomaceous earth. This type offilter generally comprises a tank which contains a plurality of tubularfilter elements 41. The tubular filter elements are positionedthroughout the tank cross-section, each comprising a mesh tube closed atits bottom end and open at its upper end for communication with theupper outlet chamber 43 of the filter. The tank has a conical lowersection terminating in an outlet connection 46 by which the tank may bedrained by way of a line 42 controlled by a drain valve 44. An outletconnection 48 communicates with the outlet chamber 43 of the filter andis connected to a clean water storage tank or reservoir (not shown) by aline 50 controlled by a valve 52. The clean water may be pumped fromthis storage tank or reservoir for use.

The line 38 has a control valve 54 connected therein adjacent to theoutlet of detention tank 10 and a control valve 56 connected thereinadjacent to the inlet to the filter 40. Line 38 also has a throttlevalve connected therein upstream of the valve 56. A pump 60 is providedupstream of valve 58 for delivering the contents of line 38 into thefilter 40. Line 26 communicates with line 38 at a location between pump60 and valve 54.

A precoat tank 62 is provided and contains a precoat slurry ofdiatomaceous earth. A mixer 64 is provided for agitating the contents oftank 62. The precoat slurry is delivered to the inlet of the filter 40through a line 66, which is connected to the suction inlet of an eductor68 and has a control valve 70 connected therein, and a line 72 which isconnected to line 38 upstream of the filter inlet and is also connectedto line 26 at its opposite end. Line 72 has a control valve 74 connectedtherein downstream of the eductor 68. Thus, liquid flowing from theclean Water storage tank 30 through line 26, line 72, and eductor 68draws liquid from the precoat tank 62 and delivers the same to thefilter 40. The precoat slurry in tank 62 contains a filter aid ofdiatomaceous earth. The precoating operation involves the feeding of alarge amount of filter aid into the filter in a short time to form aprecoat of about one-sixteenth of an inch on the filter elements. Thediatomaceous earth bridges the openings 02k the filter elements andbuilds up a precoating of filter c e.

Line 50 has connected thereto a line 76 which is com nected to the lowerportion of an automatic vent valve 78 of the float type which closesafter the liquid therein reaches a certain level and permits the escapeand entry of the air when the liquid is below the shut-off level. Arecirculating line 80, which has a control valve 82, is connectedbetween the lines 50 and 38 to provide communication therebetween forrecirculation through the filter 40 as will be described hereinafter. Abackwashing line 84 is connected between line 50 and line 38 at a pointdownstream of the pump 60 to provide communication between lines 50 and38 for backwashing the filter 40 as will be described hereafter. Abackwash valve 86 is connected in line 84 to control the flowtherethrough.

In the operation of the apparatus in accordance with this invention, theraw water is delivered continuously to the tank through line 12 withinlet valve 14 being open. The body feed slurry in tank 16, whichcomprises preflocked diatomaceous earth and a metal cation flocculatingagent, preferably iron sulfate, is fed continuously into the raw waterthrough line 20, eductor 18, valve 28, and line 24 by the action of theclean water passing through the eductor 18 by way of lines 26 and 24.Within tank 10 the metal cation-protein reaction takes placeinstantaneously forming a metal-virus complex which aggregates to form aprecipitate. While the flow is continuous through tank 10, the rawwater, diatomaceous earth and iron sulfate remain in the tank 10 for anaverage detention time of from two to ten minutes in order to secureadequate admixture thereof and to permit aggregation of the metal-viruscomplex to a size large enough to be filtered by the precoateddiatomaceous earth filter 40.

The contents of tank 10 are delivered to the filter 40 through line 38by the operation of pump 60, valves 54 and 56 being open and throttlevalve 58 being set to the desired flow rate. Prior to this, thefiltering elements have been precoated with diatomaceous earth whichprevents any virus-laden aggregates from reaching the clean inside ofthe filter tubes. Thus, the virus is removed from the water by thefiltering action of the precoat layer and the clean filtrate isdelivered through line 50 and valve 52 to the clean storage tank orreservoir. During this filtering operation, only the valves 54, 58, 56and 52 are open, the remaining valves being closed. The filteringoperation will continue until the size of the filter cake on thefiltering elements prevents an efiicient filtering opera tion by reasonof the excessive pressure drop across the filter cake.

The filter must then be renewed to place the same in condition for asubsequent filtering operation. It is important that this renewalprocedure be such that none of the virus salts can pass through thefiltering elements since these salts are equally as dangerous as thevirus.

The first step in renewing the filter coating comprises pressurizationof the filter. During this step, all the valves are closed with theexception of valves 54, 56 and 58. The pump 60 is then operated todeliver liquid into the filter 40 and, since the outlet valve 52 isclosed, air is trapped in the upper end of outlet chamber 43 above theoutlet connection 48 and is compressed by the action of the pump 60.

The next step is known as the bump and drain step during which all ofthe valves are closed with the exception of inlet valve 54, 56 and drainvalve 44. When the valve 44 is opened, the compressed air in the upperend of the filter 40 provides a sudden high velocity surge of the liquidthrough the filter tubes in a reverse flow direction thereby to dislodgethe filter cake therefrom. The dislodged filter cake containing thevirus salts will thus be washed outwardly through the drain line 42.

The next step is to fill and pressurize the filter 40. During this steponly the valves 32, 58 and 86 are open. Pump 60 is operated to drawclean liquid from tank 30 and pump the same through valve 58, line 84,and valve 86 to fill and pressurize the filter 40.

The next step is known as the htunp and rinse step which involves theopening of the drain valve 44 whereby there is a sudden surge of liquidreversely through the filter tubes and the liquid contained in tank 40passes through the drain line 42. This second sudden surge through thefilter tubes is to insure that all of the filter cake is removed fromthe filter tubes. The rinsing of the filter is continued since thevalves 32, 58 and 86 remain open. Thus, clean water passes from the tank30 through lines 26, 38, 84, 50 and connection 48 through the filtertubes into the inlet chamber of the filter and outwardly through thedrain line 42. This rinsing serves to clean the interior of the filter40 and remove any small particles of filter cake which may not have beenremoved by the previous draining steps. It may be noted that all of therinsing and filling is carried out by means of clean water. Thus, thereis no danger that the outlet side of the filtering elements will becomecontaminated.

The next step is to completely drain the filter 40. During this step thevalves 56 and 86 are closed to prevent any filling of the tank 40 andthe drain valve 44 is open to permit complete draining of the filter 40.

The next step is to rinse and drain the filter. During the initialportion of this step, the pump 60 is operated with the valves 32, '58,86 and 44 open. Thus, clean water is passed from the clean water tank 30through lines 26, 38, 84, 50 and connection 48 through the filter andout through drain line 42 thereby to backwash the filter again. At theend of this step, valve 86 is closed whereby the liquid in filter 40will completely drain therefrom through line 42, air entering throughvent 78. This final rinsing and draining provides additional insurancethat the filter 40 is free of contaminated filter cake.

The next step is that of precoating in which all of the valves areclosed with the exception of valve 70 and valve 74. Thus, clean liquidpasses through line 26, eductor 68 and line 72 to Withdraw theprecoating slurry from tank 62 through line 66 and valve 70 and deliverthe same into the filter 40. This step involves injecting a presetamount of diatomaceous earth into the filter 40 to partially fill thesame.

The next step is filling and recirculation, during which the valves 32,58, 56 and 82 are the only valves which are open. Pump 60 is operated todraw clean liquid through lines 26 and 38 and pump the same into thefilter 40 from which the liquid passes through line 50 into line whichreturns the liquid to line 38 for recirculation by the pump 60. The pump60 serves to recirculate the precoat suspension until all of the precoatis deposited on the filter tubes. During the filling and recirculatingstep, clean liquid is drawn through lines 26 and 38 and delivered intothe system until the filter 40 is filled.

In the precoating step and in the initial stages of the filling andrecirculating step, filter aid will pass through the filter elementsinto the filter outlet chamber until a suflicient depth of precoat isformed thereon. The recirculating step serves to allow the filter aid tobridge the openings in the screen and to form a filter cake. Clean Wateris used for recirculating since there will not be any effectivefiltering until the precoat layer is built up on the filter tubes. Therecirculating is continued until all of the filter aid is deposited onthe precoat layer. The filter is now ready for the filtering step as wasdescribed previously.

The renewal of the filter cake on the filtering elements takesapproximately fifteen minutes, so that the filtering is only interruptedfor a short period of time. It will be apparent that all of thesequential operations of the valves described above may be accomplishedby a suitable control system which will operate automatically. Therenewal operation described above insures that there will be nocontamination of the inlet side of the filter 40 by reason of theblowdown of the tubes and the rinsing steps described above which areaccomplished by the use of clean water.

An alternate mode of operation may involve the introduction of the metalcation flocculant to raw water as it leaves the detention tank. Thus,only the pre-flocked diatomaceous earth is added to the raw water in thedetention tank. In this system reliance is placed on the prefl-ockeddiatomaceous earth to form aggregates consisting of suspended particlesin the raw water. When the metal cation flocculant is subsequentlyintroduced, the metalvirus complex will be entrapped in these aggregateswhile going through the filter pump, the filter piping and the interiorof the filter 40 prior to reaching the filtering elements. Theaggregates will then be removed from the water by the operation offilter 40.

It may be noted that the virus removal method in accordance with thisinvention should not ordinarily be used without adequate chlorination.This invention is primarily used as a supplementary safeguard withrespect to the viruses.

As will be evident, various modifications of details may 'be madewithout departing from the scope of the invention as defined by thefollowing claim.

What is claimed is:

The method of removing virus from water which comprises the steps ofdelivering raw water to the inlet of a filter, adding a body feed ofdi-atomaceous earth to the raw Water prior to entrance thereof into thefilter, adding a metal cation flooculating agent to the raw water priorto entrance thereof into the filter whereby a metal-virus complex isformed, maintaining said mixture of said raw water, said body feed andsaid flOcculating agent a time sufiicient to permit the formation ofaggregates to a size large enough to be filtered from said raw water bysaid filter, said aggregates comprising metal-virus complex particles,passing said mixture through said filter for removing said aggregatesfrom the water, said filter being of a type having a filtering mediumtherein dividing the filter into an inlet chamber and an outlet chamberand having a layer of filter cake adhering to the inlet side of thefiltering medium for removing the particles from the raw water duringfiltration, and renewing the filter cake on said filtering medium aftera filtering run, said last-named step comprising the sequential steps ofdislodging the filter cake from said filtering medium and removing thefilter cake from the filter; said filter cake dislodging and removalcomprising the sequential steps of pressurizing the filter, suddenlyreleasing said pressure and draining the filter through a drain linecommunicating with the inlet chamber, pressurizing the filter again,suddenly releasing said pressure and rinsing the filter with clean Waterby passing clean water into the filter outlet chamber, from said outletchamber through said filtering medium into said inlet chamber, and fromsaid inlet ch-amber into a drain line, and draining the filter inpreparation 'for precoating; adding a precoating slurry to the inletchamber of said filtering medium, and recirculating said preooatingslurry by recirculating clean water through said filter until aprecoating layer is built up on the inlet side of said filtering medium.

References Cited by the Examiner UNITED STATES PATENTS 914,887 3/09Schultze 210- 935,695 10/09 Schultze 210-42 X 2,468,188 4/49 Frankenhoif210- 2,652,1 52 9/53 Frankenhofi 2 10-75 2,862,622 12/58 Kircher et al.21075 X OTHER REFERENCES Babbitt et al.: [Efiect of Body Feed on theFiltration of Water Through 'Diatomite, Univ. Ill. Eng. Expt. Sta. Bull.No. 425, 1954, 40 pp., also cited in Chem. Abst., vol. 49, 1955, page4914.

Clarke et al.: Enteric Viruses in Water, Jour. AWWA, October 1959, vol.51, pp. 1299 1317.

Pettersen: Automatic "Diatomaceo-us-Earth Filters, Jour. New EnglandWater Works Assoc., vol. 74, September 1960, pp. 245-249.

MORRIS O. WOLK, Primary Examiner.

